Figure 6.

Electrophysiological and pharmacological properties of voltagegated Na⁺ currents (I_Na(V)) in human pulmonary artery smooth muscle cells (PASMC). Cells are dialyzed with a Cs⁺-containing pipette solution [Table 1]. (a) Representative currents were elicited by depolarizing the cell to from a holding potential of –70 mV to test potentials between –80 mV and +80 mV (protocol at bottom). Upper left inset: Steady-state activation and inactivation of currents occurred within <5 ms and <16 ms, respectively. Lower right inset: Summarized I_Na(V) I-V relationship. (b) Currents were evoked by a step depolarization to 0 mV from different conditioning potentials (-120 mV and -20 mV) applied for 10 s prior to the test depolarization (left). Voltage-dependent steady-state availability (I/I_max) and normalized conductance-voltage relationship (g_Na/g_{Na, max}) of the peak I_Na(V) amplitude. The I/I_max and g_Na/g_{Na, max} curves were best fi tted using exponential and Boltzman equations, respectively. (c) I_Na(V) is completely suppressed by equimolar replacement of extracellular Na⁺ with N-methyl-D-glucamine (NMG) or extracellular application of 1 μM tetrodotoxin. Currents were elicited by step depolarizations from –70 mV to 0 mV